[PATCH] D18911: ELF: Emit .eh_frame_hdr entries for FDEs with duplicate PCs.

[Rafael Espíndola via llvm-commits]

Lgtm.
On Apr 9, 2016 15:25, "Peter Collingbourne" <peter at pcc.me.uk> wrote:

> pcc updated this revision to Diff 53146.
> pcc added a comment.
>
> Set FDE count in .eh_frame_hdr correctly instead
>
>
> http://reviews.llvm.org/D18911
>
> Files:
>   ELF/OutputSections.cpp
>   test/ELF/eh-frame-hdr-icf.s
>
> Index: test/ELF/eh-frame-hdr-icf.s
> ===================================================================
> --- /dev/null
> +++ test/ELF/eh-frame-hdr-icf.s
> @@ -0,0 +1,27 @@
> +# REQUIRES: x86
> +
> +# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t
> +# RUN: ld.lld %t -o %t2 --icf=all --eh-frame-hdr
> +# RUN: llvm-objdump -s %t2 | FileCheck %s
> +
> +# CHECK: Contents of section .eh_frame_hdr:
> +# CHECK-NEXT: 101a0 011b033b b4ffffff 01000000 600e0000
> +#                                     ^ FDE count
> +# CHECK-NEXT: 101b0 e8ffffff 00000000 00000000
> +#                   ^ FDE for f2
> +
> +.globl _start, f1, f2
> +_start:
> +  ret
> +
> +.section .text.f1, "ax"
> +f1:
> +  .cfi_startproc
> +  ret
> +  .cfi_endproc
> +
> +.section .text.f2, "ax"
> +f2:
> +  .cfi_startproc
> +  ret
> +  .cfi_endproc
> Index: ELF/OutputSections.cpp
> ===================================================================
> --- ELF/OutputSections.cpp
> +++ ELF/OutputSections.cpp
> @@ -733,23 +733,25 @@
>  template <class ELFT> void EhFrameHeader<ELFT>::writeTo(uint8_t *Buf) {
>    const endianness E = ELFT::TargetEndianness;
>
> +  uintX_t EhVA = Sec->getVA();
> +  uintX_t VA = this->getVA();
> +
> +  // InitialPC -> Offset in .eh_frame, sorted by InitialPC, and
> deduplicate PCs.
> +  // FIXME: Deduplication leaves unneeded null bytes at the end of the
> section.
> +  std::map<uintX_t, size_t> PcToOffset;
> +  for (const FdeData &F : FdeList)
> +    PcToOffset[getFdePc(EhVA, F)] = F.Off;
> +
>    const uint8_t Header[] = {1, DW_EH_PE_pcrel | DW_EH_PE_sdata4,
>                              DW_EH_PE_udata4,
>                              DW_EH_PE_datarel | DW_EH_PE_sdata4};
>    memcpy(Buf, Header, sizeof(Header));
>
> -  uintX_t EhVA = Sec->getVA();
> -  uintX_t VA = this->getVA();
>    uintX_t EhOff = EhVA - VA - 4;
>    write32<E>(Buf + 4, EhOff);
> -  write32<E>(Buf + 8, this->FdeList.size());
> +  write32<E>(Buf + 8, PcToOffset.size());
>    Buf += 12;
>
> -  // InitialPC -> Offset in .eh_frame, sorted by InitialPC.
> -  std::map<uintX_t, size_t> PcToOffset;
> -  for (const FdeData &F : FdeList)
> -    PcToOffset[getFdePc(EhVA, F)] = F.Off;
> -
>    for (auto &I : PcToOffset) {
>      // The first four bytes are an offset to the initial PC value for the
> FDE.
>      write32<E>(Buf, I.first - VA);
>
>
>
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